1. Field of the Invention
The present invention relates to a detector element array for an optical position measuring instrument.
2. Description of the Related Art
Known position measuring instruments typically include a scale as well as a scanner unit that can be moved relative to the scale in a measuring direction. The scanning unit and the scale are connected to objects whose relative and/or absolute position to one another is to be determined. In the case of a length measurement, the scale is embodied as a linear ruler, with a graduation extending in the measuring direction; in the case of a rotational measurement, the scale is embodied as a graduated plate with a circular-annular graduation. As a rule, in addition to one or more light sources and optical elements, such as lenses, scanning gratings, etc., the scanner unit further includes a detector arrangement. Via the detector arrangement, in the case of an incremental position measuring instrument, a periodic fringe pattern is scanned in a detector plane and is modulated as a function of the relative motion of the scale and the scanner unit. At the output of the detector arrangement, scanning signals modulated as a function of displacement are available for further processing in a downstream electronic unit.
In the detector arrangement, so-called detector element arrays are increasingly used. Such detector element arrays include a plurality of narrow, usually rectangular photodiodes, which are disposed adjacent one another in the measuring direction and are suitably interconnected. Typically, those photodiodes that while scanning the scale furnish in-phase scanning signals are interconnected.
However, the design and adaptation of such detector element arrays to different scanning configurations involves relatively major effort and expense. Therefore, there has long been the need to provide a detector element array of this kind for the most various scanning configurations, to which the detector element array can be adapted flexibly.
For instance, from European Patent Disclosure EP 1 308 700 A2 of the present Applicant, it is known that with the aid of a suitably embodied detector element array, scales with a different graduation period or resolution can be scanned. Moreover, in European Patent Disclosure EP 1 630 528 A2, it is disclosed how, again with the help of a single detector element array, circular scales with different radii can be scanned. In both cases, a detector element array with elongated photodiodes is provided, and the photodiodes are adaptable to various scanning configurations by means of suitable interconnection. The adaptability of the particular detector element arrays to various scanning configurations, however, is possible to only a limited extent.
From German Patent DE 197 54 626 C2 in the same generic field, on which the preamble to claim 1 of the present application is based, a programmable, optically sensitive circuit is furthermore known which enables an even more clearly flexible design of a detector element array for various scanning configurations. To that end, the corresponding circuit or the detector element array has a matrix-like arrangement of individual detector elements and optically sensitive components. In the exemplary embodiments shown, each detector element is associated with four switches, via which each detector element is selectively connectable to four detector elements that are directly adjacent it horizontally and vertically. Each switch is moreover associated with one memory element, in which information can be stored that indicates with which detector elements, via the respective switches, the respective detector element in the established scanning configuration is connected. The provisions proposed in this reference do make even further-improved flexible adaptation of the detector element array to various scanning configurations possible, but because of the many switches and memory elements, it necessitates relatively high effort and expense for circuitry. For instance, interconnecting two diagonally adjacent detector elements can be done only via a plurality of requisite switches and programmable switching devices. Moreover, because of the complicated circuit, the number of available detector elements per unit of surface area decreases; that is, there is only a relatively low resultant pixel density.
SUMMARY AND OBJECTS OF THE INVENTION
It is therefore an object of the present invention to disclose a detector element array for an optical position measuring instrument which has a high pixel density, is adaptable flexibly to the most various scanning configurations, and does not require major effort and expense for circuitry.
This object is attained according to the present invention by a detector element array for an optical position measuring instrument, by way of such array a fringe pattern resulting in a detector plane can be converted into electrical scanning signals. The detector element array includes a plurality of light-sensitive detector elements disposed in matrix-like fashion in rows and columns. The plurality of light-sensitive detector elements include a first detector element in a first column of the columns, a second detector element in the first column that is adjacent to the first detector element and a third detector element in a second column of the columns that is adjacent to the first column, wherein the third detector element is diagonally adjacent to the first detector element. The detector element array includes a first switch that selectively directly connects the first detector element with the second detector element and a second switch that selectively directly connects the first detector element with the third detector element. The detector element array includes a memory element associated with the first detector element, wherein memory element information is stored in the memory element that indicates which of the second and third detector elements is connected to the first detector element in an established scanning configuration, wherein no more than the first and second switches are associated with the memory element
According to the present invention, it is now provided that in particular the number of required switches and thus also of the necessary memory elements per detector element be reduced markedly, in that only direct connectability of different detector elements, to a limited extent, is contemplated. This is possible because it is fundamentally known which fundamental geometries the scanned fringe pattern can have in the various instances of use. In the case of a length measuring device, a parallel fringe pattern is as a rule involved; in the case of a rotational measuring device, typically there is a fringe pattern with angularly disposed fringes. Accordingly, it is sufficient according to the present invention to limit the direct connectability of the detector elements via the switches to these two basic scanning configurations. In particular with regard to scanning an angular fringe pattern, a direct connectability of diagonally adjacent detector elements via a corresponding switch is contemplated.
Thus, as an advantage of the version according to the present invention, in comparison to the prior art, the result is a detector element array of considerably less complexity in terms of circuitry; the number of switches and detector elements as well as memory elements required can be reduced markedly. Moreover, because of the reduced circuit complexity, a higher pixel density is attainable than in arrangements in accordance with the prior art; that is, in the final analysis, substantially increased optical resolution in scanning is obtained. On account of the more-favorable ratio of the available detector element area to the required area of the memory elements and switches, a higher photocurrent yield per unit of detector element area also results. Thus the scanning produces better signal quality for the same total area of the detector element array.
It should furthermore be mentioned that the detector element array of the present invention can naturally be used not only in connection with incremental position measuring instruments and periodic graduations but also with absolute position measuring instruments, in which a pseudo-random code is for instance employed for position determination.
The detector element array according to the present invention for an optical position measuring instrument, by way of which array a fringe pattern that results in a detector plane can be converted into electrical scanning signals, includes a plurality of light-sensitive detector elements disposed in matrix-like fashion in rows and columns. At least some of the detector elements are associated with no more than two switches, by way of which the various detector elements are selectively connectable to one or more adjacent detector elements. At least some of the detector elements with associated switches are associated with a memory element, in which information can be stored that indicates which adjacent detector elements, via the no more than two switches, the particular detector element is directly connected to in an established scanning configuration. Via the two switches, selectively, a direct connection to an adjacent detector element in the same column and/or a direct connection to a diagonally adjacent detector element in an adjacent column of an adjacent row can be made.
Advantageously, laterally adjacent to the detector element array, a plurality of connecting lines are disposed, with which a respective group of detector elements, connected via the switches, can be connected.
It is possible here for the detector elements of one group to generate respective in-phase scanning signals by scanning the fringe pattern.
In one possible embodiment, a channel multiplexer is disposed between the connecting lines and the detector element array, by way of which channel multiplexer the connected detector elements of the groups with in-phase scanning signals can each be switched to the same connecting line.
The detector elements can be interconnected in such a way that four scanning signals with a phase offset of 90° are located on four connecting lines, or three scanning signals phase-offset by 120° are located at three connecting lines.
It is possible that each memory element is connected to the two switches via a respective control line.
Each memory element can have one inverting and noninverting output, and each of the outputs can be connected to a control line.
Advantageously, programming lines can be disposed between the columns and rows of the detector elements and for triggering the memory elements can be connected to these memory elements in order by way of them to actuate the switches selectively.
For scanning a periodic fringe pattern including parallel fringes, only detector elements in one column can be connected to one another via the switches.
For scanning a periodic fringe pattern including angularly disposed fringes, the detector element array can have two halves, embodied mirror-symmetrically to an axis of symmetry, and looking from the direction of the axis of symmetry,                in a left half, via the two switches, selectively,                    a connection can be made with an adjacent detector element in the same column, and/or            a connection can be made with an adjacent detector element in an adjacent column on the left of a row above it and adjacent to it, and                        in a right half, via the two switches, selectively,                    a connection can be made with an adjacent detector element in the same column, and/or            a connection can be made with an adjacent detector element in an adjacent column on the right of a row above it and adjacent to it.                        
The memory element can be embodied as one of the following elements: PROM, EPROM, EEPROM, FRAM, MRAM, SRAM, DRAM.
The detector elements can all have an identical outline.
It is possible for the detector elements of adjacent rows to be aligned with one another.
Moreover, it is alternatively possible for the detector elements of adjacent rows to be disposed with a defined offset spacing in the direction in which the rows extend.
In one possible embodiment, the switches and memory elements can be disposed at least partly inside the area of the detector elements.
Moreover, precisely one memory element can alternatively be associated with each switch, for triggering.
Preferably, a position measuring instrument is equipped with a detector element array according to the present invention.
Further details and advantages of the present invention will now be explained in the ensuing description of exemplary embodiments in conjunction with the drawings.
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